Conventionally, as one method of improving a lithography margin of an exposure pattern (main pattern) in the semiconductor lithography technology, there is a layout design using auxiliary patterns (SRAF: Sub-Resolution Assist Feature).
When generating a mask pattern, SRAFs are desirably placed around a main pattern in a state where the SRAFs are not transferred onto a substrate when performing a lithography process. Moreover, SRAFs are desirably placed in a short time while improving a lithography margin as much as possible.